The disclosed invention relates to ink jet printing systems that employ replaceable consumable parts including ink cartridges, and more particularly to mechanisms for estimating the amount of ink remaining in an ink cartridge.
The art of ink jet printing is relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines have been implemented with ink jet technology for producing printed media. Generally, an ink jet image is formed pursuant to precise placement on a print medium of ink drops emitted by an ink drop generating device known as an ink jet printhead. Typically, an ink jet printhead is supported on a movable carriage that traverses over the surface of the print medium and is controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to a pattern of pixels of the image being printed.
Some known printers make use of an ink container that is separably replaceable from the printhead. When the ink container is exhausted it is removed and replaced with a new ink container. The use of replaceable ink containers that are separate from the printhead allow users to replace the ink container without replacing the printhead. The printhead is then replaced at or near the end of printhead life, and not when the ink container is replaced.
A consideration with ink jet printing systems that employ ink containers that are separate from the printheads is the general inability to predict an out of ink condition for an ink container. In such ink jet printing systems, it is important that printing cease when an ink container is nearly empty, with a small amount of stranded ink. Otherwise, printhead damage may occur as a result of firing without ink, and/or time is wasted in operating a printer without achieving a complete printed image, which is particularly time consuming in the printing of large images which often are printed in an unattended manner on expensive media.
A known approach to estimating remaining ink volume involves immersing electrodes in an ink volume and measuring a resistance path through the ink. Considerations with this approach include the complexity of incorporating electrodes in an ink container, and the variation of electrical properties with ink formulation.